Because of the substantial size and weight penalties, plus aperture blockage, associated with the use of parabolic reflector antennas, communication system users are increasingly turning to reduced mass antenna arrays for high gain applications, such as, but not restricted to power-limited satellite communication terminals. A typical high gain axial mode helical antenna array may employ a plurality of spaced apart identical antenna elements, the gain of each of which is less than that of the array. Each of the elements of the array is summed by a shared signal distribution network, through which the antenna beam or radiation pattern may be controllably steered or scanned relative to the antenna's boresight axis.
A shortcoming of an antenna array of high gain antenna elements spaced sufficiently far apart to avoid mutual coupling is the presence of grating lobes of substantial magnitude, which perturb the desired sensing direction of the antenna's main beam. In addition, since grating lobes represent directivity in unwanted directions, they may reduce the effective antenna gain in the desired direction. Unfortunately, if the array elements are placed relatively close to one another, in an effort to reduce or eliminate the grating lobe problem, mutual coupling effects between the more closely spaced elements will modify the radiation patterns of the antenna elements; in an unpredictable manner, thereby distorting the composite pattern of the array.